Generally, the distribution of commodities is performed in such a way that a commodity seller purchases commodities from a commodity provider at predetermined prices, and resells the commodities to purchasers at prices obtained by adding costs required to distribute, keep and sell the commodities and sales profits to the purchase prices of the commodities. Such selling of commodities has been primarily performed in retail stores, such as agents, stores, discount stores and department stores. A commodity seller makes efforts to continuously maintain transactions between commodity purchasers and the commodity seller through the use of a method of selling commodities while issuing coupons each corresponding to a certain percentage of the price of a commodity sold or applying certain discount rates to favored clients or clients purchasing a considerable number of commodities. However, such a typical selling method is problematic in that discount rates must be differently applied depending on profits generated by respective commodities, and the contribution levels of commodity purchasers for business activities cannot be precisely calculated, so that compensatory policies, such as the application of discount rates to commodity purchasers, cannot be precise and scientific. Therefore, indisputable motives for allowing the commodity purchasers to maintain business relations with the commodity seller cannot be induced. Further, in the case of the method of issuing coupons depending on the prices of commodities sold, there are problems in that it is inconvenient for each commodity purchaser to carefully manage coupons, and profits obtained by the commodity purchaser through the coupons are typically small, so that this method is not sufficient to induce continuous business relations as in the above-described case.
Recently, due to the rapid development of the Internet, electronic commerce through the Internet has been actively performed. Electronic commerce through the Internet is advantageous in that preferences and contribution levels of commodity purchasers can be precisely evaluated through member subscription and a database of sales records, as well as convenience in purchasing and selling commodities and reduction of distribution costs, and compensatory policies for preferred members due to the evaluated preferences and contribution levels are carried out, thus maintaining continuous business relations. However, such compensatory policies for preferred members or simple discounts of certain percentages of the selling prices of commodities are not sufficient to continuously guarantee profits of commodity purchasers, thus preventing continuous business relations between the commodity purchasers and the commodity seller from being reliably maintained.